This paper presents a robust online denoising algorithm for use in the online, instantaneous detection of changing harmonic signals. This algorithm uses a classical time correlation function (scalar product). For instantaneous frequency detection, a short window is considered. It is known that cleaned signals are required to determine the correct correlation between short signals. The measured signal is cleaned by the proposed noise removal algorithm, which uses wavelet packets. The proposed cleaning method avoids classical thresholding techniques. Computer simulations that validate the procedure are shown.